The invention relates to a corneal resurfacing apparatus. It has application to the cornea of any eye, but would typically be used on the human eye.
The refractive power of the cornea may be changed by altering the curvature of its anterior surface. For example, nearsightedness, farsightedness and/or astigmatism and other eye focusing problems can be adjusted by reshaping the cornea. Contact lenses seated on the cornea adjust visual acuity by reshaping the cornea. However, where contact lenses temporarily alter the anterior corneal curvature while they are being worn, the apparatus of the invention has as its purpose the permanent alteration of this curvature.
The concept of grinding the anterior corneal surface to alter its curvature is disclosed, for example, in Mueller and O'Neill, "Some Experiments on Corneal Grinding", which appeared in Experimental Eye Research (1967), 6, 42-47, a paper published by two researches in London, England. However, an apparatus for corneal resurfacing or grinding was not proposed by these researchers or by other prior art of which I am aware.
A rotating grinding disc which rotates around a single axis and is held stationary over the surface that it is grinding does not produce an evenly ground depression. Instead, the depression produced by such a disc has a uniform annular maximum depression toward its periphery and a gradually shallower annular depression moving toward its center. This results from the geometry of the disc, as more abrasive material passes over a particular location toward the periphery of the disc than toward the center of the disc in each revolution of the disc. To achieve a more uniform grinding depression, the Mueller and O'Neill article proposes providing a grinding lap which simultaneously rotates around two mutually perpendicular axes, one generally along the visual axis of the eye and the other perpendicular to the visual axis.
But, a corneal resurfacing apparatus requires more than a grinding lap. The patient's head must be held stationary as his cornea is being ground. Furthermore, the eyeball readily shifts in its socket and it could be quite harmful if such shifting occurs while the cornea is being ground. Further, in order that the grinding program might be accurately followed and that the cornea be properly surfaced, the eye must be precisely and properly aligned and its visual or optical axis must be properly aligned with respect to the placement of the grinding disc. Finally, as the cornea is quite thin and as the grinding must be done with great precision, the grinding program must be controlled and must grind only to a predetermined depth.
Other techniques are known for correcting refractive errors of the cornea. These have involved incisions in the cornea, or knife cutting away of part of the cornea to alter its shape or to temporarily remove that part of the cornea to work on it and then replace it in the eye, or replacement of part of the cornea with some substitute, etc. See for example, Sato, T. (1953) Am. J. Opthal. 36:823; Barraquer, J. I. (1964) Archos Soc. Am. Oftal. Optom. 5:27 and (1968) J. Cryosurg. 1:39; Ainslie, D. (1969) Trans. Opthal. Soc. U. K. 89:647; Littman, H. (1967) Archos Soc. Am. Oftal. Optom. 6:103; Krawicz (1964) Am. J. Opthal. 57:828 and (1965) Klinoczna 35:13. But, none of these techniques so closely controls the shape of the anterior surface of the cornea as the present invention.